1. Field of the Invention
The present invention relates to cross flow fans and air conditioners, and more particularly, to a cross flow fan with more than two unit successive fans, and an air conditioner fitted with the same.
2. Background of the Related Art
The air conditioner is an appliance for cooling/heating a room by using heat absorption/discharge from/to an environment in phase change of a working fluid.
In general, the air conditioner is provided with an indoor unit and an outdoor unit. The outdoor unit is provided with an outdoor heat exchanger, an outdoor fan, and a compressor, and the indoor unit is provided with an indoor heat exchanger and a fan.
The compressor, the outdoor heat exchanger, and the indoor heat exchanger are connected with refrigerant pipe, and the refrigerant circulates the compressor, the outdoor heat exchanger, the indoor heat exchanger, and the compressor in succession through the refrigerant pipe. The indoor heat exchanger produces cold air as the refrigerant evaporates at the indoor heat exchanger and absorbs heat from an environment, which cold air is discharged to a room space by the fan, to cool down the room.
The fan fitted to the indoor unit of the air conditioner draws air through an inlet and discharge through an outlet. The air drawn into the indoor unit through the inlet is deprived of heat to become cold air as the air passes through the indoor heat exchanger, and discharged to the room space through the outlet.
Meanwhile, the fans employed for the air conditioners are sirocco fans, propeller fans, turbo fans, and cross flow fans, wherein the cross flow fans are mostly used in small sized air conditioners each having the indoor unit and the outdoor unit separated from each other.
The cross flow fan is provided with an annular rim, and a plurality of impellers arranged along a circumference of, and vertical to the rim. The cross flow fan is fitted to the indoor unit, so that the impellers draw air at an inlet side in a circumferential direction and discharge the air in the circumferential direction at an outlet side in the circumferential direction as the impellers are rotated.
In the meantime, a pressure around the impeller is varied with time at fixed intervals as the impellers rotate. Particularly, when the cross flow fan is rotated, there are sharp periodic variations of pressures in parts adjacent to a stabilizer and a rear guide. The periodic pressure variation causes noise at a particular frequency, according to which principle, loud noise emits from the cross flow fan fitted to the indoor unit at particular frequencies as shown in FIG. 1. For reference, FIG. 1 illustrates a graph showing a result of measurement done by a computer simulation of sound pressure levels of the cross flow fan with 32 impellers, wherein it can be noted that there are significantly high sound pressures of 30 dB and 25 dB at approx. 800 Hz and 1600 Hz, respectively.
Consequently, a supplementary design of the cross flow fan is required for improving a problem of causing significantly high noises at particular frequencies when the cross flow fan rotates.